1. Field of the Invention
The present invention generally relates to medical devices, and in particular, to an improved balloon catheter and method of manufacture.
2. Description of the Related Art
Medical balloon catheters have been proven efficacious in treating a wide variety of blood vessel disorders. Moreover, these types of catheters have permitted clinicians to treat disorders with minimally invasive procedures that, in the past, would have required complex and perhaps life threatening surgeries. For example, balloon angioplasty is now a common procedure to alleviate stenotic lesions (i.e., clogged arteries) in blood vessels, thereby reducing the need for heart bypass operations.
Compliant inflatable balloons, of the type used with medical catheters, increase in diameter with increasing inflation pressure until the balloon burst pressure is reached, as is well-known to those of skill in the art. Such balloons are especially advantageous when used as a medical catheter balloon, or as the securing element of an anchorable guidewire. In both applications, the balloon must be expanded to contact the blood vessel wall. In some treatment procedures, however, the clinician does not know the precise diameter of the blood vessel segment that the balloon must contact. In these situations, the compliant expansion profile of the balloon permits the clinician to make the required contact, by application of increasing inflation pressures to cause increased balloon radial expansion until contact is achieved.
Conventional compliant expansion balloons are generally made of elastomeric materials, such as latex and silicone. Balloons made of these materials utilizing conventional balloon formation techniques suffer from several disadvantages which adversely affect the balloon""s performance.
One disadvantage of conventional compliant balloons relates to their elastic response. It is desirable for catheter balloons to have a predictable inflation profile. That is, the balloon should inflate to a certain known size upon application of a specific pressure. Moreover, the balloon should exhibit good elasticity, inflating to approximately the same size upon application of the same specific pressure or volume, even after the balloon has been inflated and deflated multiple times. However, conventional compliant balloons often do not exhibit this desired elastic response, and tend to inflate to larger sizes upon application of the same specific pressure each subsequent time they are inflated. This is because each inflation stretches the balloon, and upon deflation, the balloon does not return to its original deflated size, but instead is somewhat larger. Consequently, upon each subsequent inflation, the stretched balloon inflates to a larger size than before, making it difficult for the clinician to predict the amount of pressure that must be applied to inflate the balloon to the size needed to contact the vessel.
Another disadvantage of conventional compliant balloons relates to their longitudinal expansion. As described previously, compliant balloons tend to increase in radial diameter with increasing inflation pressure. In addition, many compliant expansion balloons also tend to increase in length with increasing inflation pressure. This is an undesirable expansion characteristic, as it creates an unwanted shearing force within the blood vessel, which could lead to vessel trauma.
Accordingly, there exists a need for compliant expansion balloons for use on medical catheters, or as securing members on anchorable guidewires, which have a predictable elastic response, a predictable longitudinal expansion, and a predictable diameter, at different volumes or pressures. In addition, there is a need for methods of making such balloons.
Balloons used for angioplasty and other procedures are bonded to catheter tubular bodies. Conventional balloon bonding techniques used to mount the balloons to catheter tubular bodies include adhesive bonding and heat bonding, as known to those of skill in the art. When adhesive bonding is used, each end of the balloon is mounted to the catheter tubular body to form a fluid tight seal. An adhesive is applied to the ends of the balloon which wicks into the balloon to form a seal with the catheter tube. Typically, clamps are placed adjacent to the working area (i.e., the area within the balloon which is not bonded to the catheter and which is therefore available for inflation) to prevent adhesive flow into the working area. This technique, however, does not provide complete control of the working length because clamps are not completely effective in preventing adhesive flow into the working area. In particular, the difficulty in controlling the clamping force may allow the adhesive to wick into the working area. This creates the problems that the balloon working length may not be at the precise location desired on the catheter tubular body, and that balloon inflation may not be uniform. Thus, there is a need to control adhesive wicking of the balloon seal to control the balloon working length.
A further problem arises from the need to inflate the balloon in a uniform manner. The balloon must be centered around the catheter tube in order to allow a more uniform vessel occlusion or similar effect. Thus, there is also a need for a balloon catheter and a method for manufacturing the same wherein a balloon is centered around a catheter to allow uniform inflation of the balloon.
The present invention advantageously provides a compliant expansion balloon with an improved elastic response and reduced longitudinal expansion. In one aspect of the present invention, there is provided a longitudinally pre-stretched styrene-ethylene-butylene-styrene (SEBS) compliant catheter balloon. Preferably, the balloon is formed in part by longitudinally stretching an extruded styrene-ethylene-butylene-styrene tube such that the tube increases in length by at least 200%. More preferably, the tube increases in length by at least 600 to 900%. It is also preferred that the balloon be formed from a tube stretched at a rate of from about 10 cm/min to about 30 cm/min. Balloons of this type exhibit decreased longitudinal expansion when inflated. Preferably, the longitudinal expansion of the balloon formed in part by stretching the extruded tube is 20%-50% less than a balloon formed from an unstretched tube of identical composition.
In another aspect of the present invention, there is provided a method of making a compliant inflatable catheter balloon with reduced longitudinal expansion. The first step of the method is to provide an extruded SEBS tube having a first length and a first inner diameter. The extruded SEBS tube is then stretched longitudinally so that the tube forms a second inner diameter smaller than the first diameter, and a second length greater than the first length.
In an alternate first step, there is provided an extruded SEBS tube having a first length and a first thickness. The extruded SEBS tube is then stretched longitudinally so that the tube has a second length greater than the first length, and a second thickness which is less than the first thickness.
After the stretching process, the tube is preferably cut within two hours of the stretching step. In a preferred practice of the method, the second length is at least 600% greater than the first length, more preferably is at least 700% greater than the first length, and optimally is at least 900% greater than the first length.
In addition, it is also preferred that the second diameter be about 40% smaller than the first diameter, more preferably about 30% smaller than the first diameter.
The longitudinal stretching also preferably occurs at a rate of about 10 cm/min-30 cm/min, and takes place in an environment having a temperature of between 0xc2x0 and 90xc2x0 C.
In order to control the working length of the balloon on a catheter, at least one adhesive stop is provided on the catheter which prevents adhesive from wicking into the working length of the balloon. Preferably, a pair of thermoset tubings with an outer diameter size close to the size of the inner diameter of the balloon is inserted on the distal portion of the catheter. After the proper placement of the balloon, the adhesive is applied at the balloon""s proximal and distal ends. As the adhesive wicks to the balloon, the thermoset tubings will eventually stop the adhesive to prevent further wicking of adhesive into the balloon""s working length. So in essence, the thermoset tubings become like a barrier or stopper to control the wicking of adhesive, the seal length and working length all together. This effect not only helps maintain dimensional specifications but also helps to aid in centering the balloon around the catheter.
In one aspect of the present invention, an inflatable balloon catheter is provided comprising an elongate tubular body having proximal and distal ends with a lumen extending through the tubular body from the proximal to the distal end. An inflatable balloon with an interior volume in fluid communication with the lumen is bonded concentrically to the tubular body at its proximal and distal ends by an adhesive. The balloon has a working area within the interior volume which is not bonded to the tubular body. At least one adhesive stop is located on the elongate tubular body and within the interior volume of the balloon to prevent the adhesive from wicking into the working area of the balloon.
In another aspect of the present invention, there is provided a method of manufacturing a balloon catheter to improve centering of the balloon on the catheter. The first step of the method is to extrude a resin to form a tube having an inner and outer diameter and an inner surface. The tube is then pre-stretched to reduce the inner and outer diameters of the tube. The stretched tube is stabilized at a temperature above about 60xc2x0 C. This stabilization step ensures that a balloon mounted on a catheter will inflate in a uniform manner.